Can you tell me please if there is a formula for choosing the tabletop terrain. Page 8 of the H&H Medieval rules points me to a dedicated support section on the website but I can find no reference there.

Hi Robert,
the rules support section of the website contains hex grids which you can use to plan your layout using the terrain features available. At the club we often ask a non playing member to choose and layout terrain features from a limited selection. Players then dice for choice of table edge and first deployment.
With two players , one could selct and layout the terrain and the other have choice of table edge.

I have a selection of sketches of different terrain layouts on the grid paper which I will scan and upload as examples.

Create a table using playing card values which represent a type of terrain. Theoretically divide the surface into 4 or 6 sections and deal a card into each. For a road or river, each starts in the section where the card fell and runs to the opposite side.